1. Field of Invention
This invention relates generally to an optical logic based computing method or process and to devices and systems for practicing such methods. More particularly this invention relates to truth table based hybrid optical/electronic methods and arrangements for implementing a noncontending crossbar switch with bit-slice reconfigurability.
2. Description of Related Art
Reference may be had to a paper by A. A. Sawchuk, B. K. Jenkins, and C. S. Raghavendra entitled "Optical Crossbar Networks," IEEE Computer Magazine, vol. 20, No. 6, pp 50-60 (Jun. 1987) for general background information pertaining to N.times.N optical cross bar networks. The paper reviews six standard methods for implementing an N.times.N optical crossbar switching that is capable of connecting any of N data inputs to any of all of N output without contention. This paper also compares optical crossbar switches to electronic crossbar switches and points out that the six standard optical implementations are capable of relatively high data rates and relatively slow reconfiguration rates, while electronic crossbar switches are capable of somewhat slower data rates and somewhat higher reconfiguration rates. It is worth noticing that none of the electronic crossbar switches use optical fan-out from the input data lines. Also, none of the six optical techniques are based on implementation specifying N input data bits, (log.sub.2 N).times.M input control bits, and M output bits in the form of a truth table or logic array. It would be advantageous if a truth table based optical crossbar switch could be devised since such a switch would be seemingly capable of achieving both high data rates and high reconfiguration rates.
General background information with respect to the state of the art in electronic programmable logic arrays is provided in a paper by P. Robinson entitled "Overview of Programmable Hardware," Byte Magazine, vol. 12, No. 1 Jan. 1987).
Optical crossbar structures for effecting a fiber optic based version of a programmable logic array are disclosed in my above-cited co-pending patent application Ser. No. 912,353. It also disclosed hybrid optical/electronic methods for implementing a programmable logic array. The present invention extends and refines these concepts to permit the construction of an optical crossbar switch.
The use of truth tables to effect both high data rate and high reconfiguration rate noncontending optical crossbar switches is described in my paper entitled "Reconfigurable Fiber Optics and Generalized Crossbar Switches," Society of Photo-Optical Instrumentation Engineers, vol. 835, pp. 338-345 (Aug. 16, 1987). which is hereby incorporated by reference herein. This paper outlines the mathematical and logical basis for such optical crossbar switches but does not describe methods or structures for implementing same. The work described in the paper was supported, in part, by the Defense Advanced Research Projects Agency (DARPA), which has encouraged the development of improved varieties of optical crossbar switches.
To the best of my knowledge, all previous optical crossbar systems suffer from one or more important deficiencies which prevents them from achieving the theoretical advantages described in my above-cited paper. Either they do not specify N input data bits, (log.sub.2 N).times.M input control bits, and M output bits in the form of a truth table or logic array, or they do not include optical fan-out from the input data lines or they are incapable of bit-slice reconfigurability. Here bit-slice reconfigurability is defines as the ability of the crossbar switch to reconfigure its data input-output switch settings in a period that is equal to one or a relatively small number of input data bit intervals. The advantages of bit-slice reconfigurability in a crossbar switch includes high reconfiguration rates, the ability to transfer both small and large blocks of data, an increase in the effective data rate, a potential increase in the efficiency of processor level communications, and the possible use of a crossbar switch as a computational component. Thus, it would be highly desirable if one or more methods and systems could be found for implementing a globally connected optical crossbar structure with optical fan-out from the input data lines which forms an integral part of a truth table based hybrid optical/electronic crossbar switch capable of bit-slice reconfigurability.
The primary object of this invention is to provide a method and apparatus for a hybrid optical/electronic noncontending N.times.M crossbar that overcomes many of the restrictions of existing crossbar switches in terms of being able to achieve both high data rates and high reconfiguration rates.
An important object of the present invention is to achieve the abovestated primary object by providing a method and apparatus for implementing a truth table based hybrid optical/electronic noncontending N.times.M crossbar switch with bit-slice reconfigurability.
An other object of this invention is to provide a method and apparatus for a generalized structure that is capable of implementing a truth table based hybrid optical/electronic noncontending N.times.M crossbar switch with bit-slice reconfigurability.
Yet another object is to provide a method and apparatus for a truth table based hybrid optical/electronic asynchronous noncontending N.times.M crossbar switch that is effected by optoelectronic means through the sequence INVERT-OR-INVERT-OR.
One more object of this invention is to provide a method and apparatus for a truth table based hybrid optical/electronic asynchronous noncontending N.times.M crossbar switch that is effected by a combination of optoelectronic means and programmable logic devices.
Still another object is to provide a method and apparatus for a truth table based hybrid optical/electronic asynchronous noncontending N.times.M crossbar switch that is effected by a combination of optoelectronic means and multiplexers.
An additional object is to provide a method and apparatus for a truth table based hybrid optical/electronic synchronous noncontending N.times.M crossbar switch that is effected by a combination optoelectronic means, multiplexers, and memory elements.